1. Field of the Invention
This invention relates to an expansion joint for bridges over rivers, valleys or roads, more particularly to such one that is called a seamless expansion joint.
2. Prior Art
Conventional expansion joints include a finger joint which comprises a pair of comb teeth-like steels arranged between a pair of slabs opposite to each other, with each one end thereof fixed to respective opposite ends of the slabs, and a rubber joint which comprises a rubber seal interconnecting the opposite ends of the slabs to cover the clearance or idle space therebetween, and these two kinds of expansion joints have been dominantly used. However, these two kinds of expansion joints involve such drawbacks due to discontinuity of pavement surfaces on the floor boards that provides vehicles with unfavorable running face and generates uncomfortable noise.
Accordingly, in order to overcome these drawbacks, there has recently been proposed and practically used such expansion joint that is called a seamless expansion joint. A main feature of this expansion joint resides in that a composite comprising a binder and natural aggregates is laid on such notched portions of pavements as prepared over opposite ends of a pair of slabs and that the upper face of thus laid composite is made even with those of the remaining portions of the pavements (cf. for example, Japanese Patent Laying-open No. 61-191703).
Worthy to the name, the seamless expansion joint provides a favorable influence upon the vehicle's running since the composite laid on the notched portions is made even with the surface of pavements, and generates little noise since there is no gap on the running face over the clearance.
Usually, the seamless expansion point employs a composite consisting of natural aggregates and a rubber asphalt as a binder, and the role of compression resistance against vehicle load is allotted to natural aggregates embedded in plastic materials, while the elasticity against the floor boards is performed by the binder.
However, since the rubber asphalt itself has no elasticity but a plastic nature, the layer of the composite cannot resist vehicles of heavy load to result in gradual deformation which ruins the flatness of the road surface. On the other hand, since the natural aggregates lack elasticity, the elasticity of the rubber asphalt alone does not provide the road structure with sufficient elasticity.